JP6973874B2 - Super absorbent polymer and its manufacturing method - Google Patents

Description

[Mutual citation with related applications]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0139103 dated November 13, 2018 and Korean Patent Application No. 10-2019-0113734 dated September 16, 2019. All content disclosed in the literature of the application is included as part of this specification.

The present invention relates to a super absorbent polymer and a method for producing the same. More specifically, the present invention relates to a superabsorbent polymer having improved rewet properties and liquid permeability, and a method for producing the same.

A super absorbent polymer (SAP) is a synthetic polymer substance having a function of absorbing about 500 to 1,000 times its weight of water, and is a SAM (Super Absorbent Polymer) for each developer. , AGM (Absorbent Gel Material), etc. are named with different names. Superabsorbent polymers such as those mentioned above have begun to be put into practical use as sanitary tools, and are currently used in addition to sanitary products such as children's disposable diapers and sanitary napkins, as well as soil water retention agents for gardening, civil engineering, water blocking materials for construction, and sheets for raising seedlings. , As a freshness preservative in the food distribution field, and as a material for poultices.

In most cases, such superabsorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins, but for such applications, they must exhibit high absorbency to moisture and the like. Moisture absorbed by external pressure must not escape, and in addition, it is necessary to maintain good morphology even in the state of absorbing water and expanding (swelling) in volume, and to show excellent permeability. There is.

However, the superabsorbent polymer has a retention capacity (CRC), which is a physical property showing the basic absorption capacity and water retention capacity, and a pressure absorption capacity (AUP), which has a characteristic of well retaining water absorbed even under external pressure. ) Are known to be difficult to improve together. This is because if the overall crosslink density of the superabsorbent polymer is controlled to be low, the retention capacity can be relatively high, but the crosslink structure becomes coarse, the gel strength becomes low, and the absorption capacity under pressure can decrease. Is. On the contrary, when the cross-linking density is controlled to be high to improve the absorption capacity under pressure, it becomes difficult for water to be absorbed between the dense cross-linking structures, and the basic retention capacity may decrease. For the reasons described above, there is a limit in providing a superabsorbent polymer having both improved holding ability and absorption ability under pressure.

However, recently, with the thinning of sanitary materials such as diapers and sanitary napkins, higher absorption performance for superabsorbent polymers is required. Among them, the simultaneous improvement of the holding ability and the pressurized water absorption ability, which are contradictory physical properties, and the improvement of the liquid permeability have emerged as important issues.

In addition, pressure is applied to sanitary materials such as diapers and sanitary napkins depending on the weight of the user. In particular, after the super absorbent polymer applied to sanitary materials such as diapers and sanitary napkins has absorbed the liquid, some liquid absorbed by the superabsorbent polymer when pressure is applied by the weight of the user. A rewet phenomenon in which urine exudes again and a leakage phenomenon in which urine leaks can occur.

Therefore, various attempts are being made to suppress such a rewetting phenomenon. However, the actual situation is that no concrete plan that can effectively suppress the rewetting phenomenon has been presented.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a superabsorbent polymer in which rewetting and urine leakage phenomena are suppressed and a method for producing the same.

In order to achieve the above object, according to one aspect of the invention,
A step of preparing a base resin (base resin) having an acidic group and having an acrylic acid-based monomer in which at least a part of the acidic group is neutralized and an internal cross-linking agent cross-linked and polymerized (step 1);
The base resin is mixed with an inorganic filler and an epoxy-based surface cross-linking agent, the inorganic filler is first dry-mixed with the base resin, and then the epoxy-based surface cross-linking agent is dissolved in water to obtain a surface cross-linking solution. (Step 2); and a step (step 3) in which the mixture of the step 2 is heated to perform surface modification to the base resin.
The epoxy-based surface cross-linking agent contains a first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy cross-linking agent having an epoxy equivalent of 130 to 200 g / eq. Provides a manufacturing method for.

Also, according to another aspect of the invention.
A base resin containing a crosslinked polymer in which an acrylic acid-based monomer in which at least a part of an acidic group is neutralized is crosslinked and polymerized; and the crosslinked polymer is formed on the particle surface of the base resin and has an epoxy equivalent. Includes a double surface modification layer that is additionally cross-linked via two different epoxy-based surface cross-linking agents.
The surface modification layer contains an inorganic filler and contains an inorganic filler.
The two epoxy-based surface cross-linking agents include a first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy cross-linking agent having an epoxy equivalent of 130 to 200 g / eq. Provide a water-absorbent resin.

According to the highly water-absorbent resin of the present invention and the method for producing the same, it is possible to provide a highly water-absorbent resin in which the rewetting phenomenon and the urine leakage phenomenon are suppressed while exhibiting excellent water-absorbing physical characteristics.

Since the present invention can be modified in various ways and can have various forms, specific examples will be illustrated below in detail. However, this is not intended to limit the invention to any particular form of disclosure, but should be understood as including all modifications, equivalents or alternatives contained within the ideas and technical scope of the invention.

Hereinafter, a method for producing a super absorbent polymer according to an embodiment of the present invention will be described in detail.

The method for producing a superabsorbent polymer according to an embodiment of the present invention is as follows.
A step of preparing a base resin (base resin) having an acidic group and having an acrylic acid-based monomer in which at least a part of the acidic group is neutralized and an internal cross-linking agent cross-linked and polymerized (step 1);
The base resin is mixed with an inorganic filler and an epoxy-based surface cross-linking agent, the inorganic filler is first dry-mixed with the base resin, and then the epoxy-based surface cross-linking agent is dissolved in water to obtain a surface cross-linking solution. A step of mixing (step 2); and a step of raising the temperature of the mixture of the step 2 to perform surface modification on the base resin (step 3) are included.
The epoxy-based surface cross-linking agent includes a first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq, and a second epoxy cross-linking agent having an epoxy equivalent of 130 to 200 g / eq.

In the specification of the present invention, the "base resin" or "base resin powder" is a polymer in which a water-soluble ethylene-based unsaturated monomer is polymerized, dried and pulverized, and in the form of particles or powder. This means a polymer in a state where the surface modification or surface cross-linking step described later is not performed.

The hydrogel polymer obtained by the polymerization reaction of the acrylic acid-based monomer is marketed as a superabsorbent polymer which is a powdery product through steps such as drying, pulverization, classification, and surface cross-linking.

Recently, it is important to measure the diaper characteristics not only for various water-absorbing physical properties such as absorbency and liquid permeability in superabsorbent polymers, but also for how long the dryness of the surface is maintained in the situation where actual diapers are used. It is a scale.

The superabsorbent polymer obtained by the production method according to the embodiment of the present invention has excellent physical properties such as retention ability, pressure water absorption ability, and liquid permeability, exhibits excellent absorption performance, and after being swollen with salt water. The present invention has been confirmed to have the potential to effectively prevent the rewet and leak (leakage) phenomena in which urine absorbed by the super absorbent polymer is exuded again while the dry state is maintained. It came to.

In the method for producing a highly water-absorbent resin of the present invention, the monomer composition which is the raw material of the highly water-absorbent resin has an acidic group, and at least a part of the acidic group is neutralized. A monomer composition containing a monomer, an internal cross-linking agent and a polymerization initiator is polymerized to obtain a hydrogel-like polymer, which is dried, pulverized and classified to prepare a base resin (step 1). ).

This will be described in more detail below.

The monomer composition which is a raw material of the highly water-absorbent resin contains an acrylic acid-based monomer which has an acidic group and at least a part of the acidic group is neutralized, and a polymerization initiator.

The acrylic acid-based monomer is a compound represented by the following chemical formula 1.

In the chemical formula 1,
R ¹ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond.
M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt.

Preferably, the acrylic acid-based monomer contains one or more selected from the group consisting of acrylic acid, methacrylic acid and monovalent metal salts thereof, divalent metal salts, ammonium salts and organic amine salts.

Here, the acrylic acid-based monomer has an acidic group, and at least a part of the acidic group may be neutralized. Preferably, the monomer is partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like. At this time, the degree of neutralization of the acrylic acid-based monomer may be 40 to 95 mol%, 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization can be adjusted according to the final physical characteristics. However, if the degree of neutralization is excessively high, the neutralized monomer is precipitated and smooth progress of polymerization is difficult. On the contrary, if the degree of neutralization is excessively low, the absorbency of the polymer is greatly reduced. It may exhibit elastic rubber-like properties that are difficult to handle.

The concentration of the acrylic acid-based monomer can be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition containing the raw material and the solvent of the super absorbent polymer. The concentration can be adjusted as appropriate in consideration of the polymerization time, reaction conditions and the like. However, if the concentration of the monomer is excessively low, the yield of the superabsorbent polymer is low and a problem may occur in terms of economy. On the contrary, if the concentration is excessively high, a part of the monomer is precipitated or polymerized. When the water-containing gel-like polymer is crushed, there may be a problem in the process such as the crushing efficiency being shown to be low, and the physical properties of the superabsorbent polymer may be deteriorated.

In the method for producing a superabsorbent polymer of the present invention, the polymerization initiator used at the time of polymerization is not particularly limited as long as it is generally used for producing a superabsorbent polymer.

Specifically, as the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator by UV irradiation can be used depending on the polymerization method. However, even with the photopolymerization method, a certain amount of heat is generated by irradiation such as ultraviolet irradiation, and a certain amount of heat is generated by the progress of the polymerization reaction which is an exothermic reaction. Therefore, a thermal polymerization initiator is additionally included. You can also do it.

The photopolymerization initiator can be used without limitation in its composition as long as it is a compound capable of forming radicals by light such as ultraviolet rays.

Examples of the photopolymerization initiator include benzoin ether, dialalkyl acetatephenone, hydroxyyl alkylketone, phenylglycyllate, and benzyldimethylketal (Benz). One or more selected from the group consisting of acyl phosphine and α-aminoketone can be used. On the other hand, as a specific example of acylphosphine, a commercial lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethylphosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. .. More diverse photoinitiators are well documented in Reinhold Schwarm's book "UV Coatings: Basics, Recent Developers and New Applications (Elsevier 2007)" p115, and are not limited to the examples described above.

The photopolymerization initiator may be contained in a concentration of about 0.01 to about 1.0% by weight with respect to the monomer composition. When the concentration of such a photopolymerization initiator is excessively low, the polymerization rate becomes slow, and when the concentration of the photopolymerization initiator is excessively high, the molecular weight of the highly water-absorbent resin is small and the physical properties become non-uniform.

Further, as the thermal polymerization initiator, one or more selected from the initiator group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide and ascorbic acid can be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate. (NH ₄ ) ₂ S ₂ O ₈ ), and examples of azo (Azo) -based initiators are 2,2-azobis- (2-amidinopropane) dihydrochloride (2,2-azobis (2). -Amidinopropane) dihydrochloride), 2,2-azobis- (N, N-dimethylene) isobutylamizin dihydrochloride (2,2-azobis- (N, N-dimethylene) isobutyramidine dihydrochlide), 2- (carbobisisobuty) Ninitrile (2- (carbamoylazo) isobutyloniril), 2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (2,2-azobis [2- (2-imidazolin-2-yl) propane) ] Dihydrochlide), 4,4-azobis- (4-cyanovaleric acid) (4,4-azobis- (4-cyanovaleric acid)) and the like. More diverse thermal polymerization initiators are well documented in Odian's book "Principle of Polymerization (Wiley, 1981)", p203, and are not limited to the examples described above.

According to one embodiment of the present invention, the monomer composition contains an internal cross-linking agent as a raw material for a superabsorbent polymer. The internal cross-linking agent is a cross-linking agent having one or more functional groups capable of reacting with the acrylic acid-based monomer and having one or more ethylenically unsaturated groups; or substitution of the acrylic acid-based monomer. A cross-linking agent having two or more functional groups capable of reacting with a substituent formed by hydrolysis of a group and / or a monomer can be used.

The internal cross-linking agent is for cross-linking the inside of a polymer in which an acrylic acid-based monomer is polymerized, and is classified as a surface cross-linking agent for cross-linking the surface of the polymer.

Specific examples of the internal cross-linking agent include N, N'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, (meth) acrylate, and propylene glycol di (meth) acrylate. , Polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene Glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerintri (meth) acrylate, pentaeristol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, And one or more selected from the group consisting of ethylene carbonate can be used.

Such an internal cross-linking agent is contained in the monomer composition at a concentration of about 0.01 to about 1.0% by weight, and can cross-link the polymerized polymer.

In the production method of the present invention, the monomer composition of a highly water-absorbent resin may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Raw materials such as acrylic acid-based monomers having the above-mentioned acidic groups and neutralizing at least a part of the acidic groups, photopolymerization initiators, thermal polymerization initiators, internal cross-linking agents and additives are solvents. Prepared in the form of a solution of the monomer composition dissolved in.

The solvent that can be used at this time can be used without limitation in its composition as long as the above-mentioned components can be dissolved. For example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, and ethylene can be used. Glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and One or more selected from N, N-dimethylacetamide and the like can be used in combination.

The solvent may be contained in a residual amount excluding the above-mentioned components with respect to the total content of the monomer composition.

On the other hand, the composition of such a monomer composition is not particularly limited as long as it is a commonly used polymerization method by thermally polymerizing or photopolymerizing such a monomer composition to form a hydrogel-like polymer.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source, and when normal thermal polymerization is carried out, it can be carried out by a reactor having a stirring shaft such as a kneader, and photopolymerization can be carried out. When it is carried out, it is carried out in a reactor equipped with a movable conveyor belt, but the above-mentioned polymerization method is an example, and the present invention is not limited to the above-mentioned polymerization method.

As an example, as described above, a water-containing gel-like polymer can be obtained by supplying hot air or heating the reactor to a reactor such as a kneader equipped with a stirring shaft for thermal polymerization. Depending on the form of the stirring shaft provided in the reactor, the hydrogel polymer discharged to the outlet of the reactor can be in the form of a few centimeters to a few millimeters. Specifically, the size of the obtained hydrogel-like polymer varies depending on the concentration of the monomer composition to be injected, the injection rate, and the like, but usually it is a hydrogel-like polymer having a weight average particle size of 2 to 50 mm. A polymer is obtained.

Further, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the form of the normally obtained hydrogel-like polymer may be a sheet-like hydrogel-like polymer having a belt width. .. At this time, the thickness of the polymer sheet varies depending on the concentration of the monomer composition to be injected and the injection rate, but usually, a sheet-like polymer having a thickness of about 0.5 to about 5 cm can be obtained. It is preferable to supply the monomer composition to the above. When the monomer composition is supplied to such an extent that the thickness of the sheet-shaped polymer is excessively thin, it is not preferable because the production efficiency is low, and when the thickness of the sheet-shaped polymer exceeds 5 cm, the thickness is excessively thick. Due to the fact that the polymerization reaction is not carried out equally over all thicknesses.

At this time, the normal water content of the water-containing gel-like polymer obtained by such a method can be about 40 to about 80% by weight. On the other hand, in the entire specification, the "moisture content" is the content of water in the total weight of the water-containing gel-like polymer, and is the value obtained by subtracting the weight of the dry polymer from the weight of the water-containing gel-like polymer. means. Specifically, it is defined by a value calculated by measuring the weight loss due to evaporation of water in the polymer in the process of raising the temperature of the polymer by infrared heating and drying. At this time, the drying condition is a method in which the temperature is raised to about 180 ° C. at room temperature and then maintained at 180 ° C., the total drying time is set to 20 minutes including 5 minutes in the temperature rise step, and the water content is measured.

Next, a step of drying the obtained hydrogel-like polymer is performed.

At this time, if necessary, a step of coarse pulverization before drying is further performed in order to increase the efficiency of the drying step.

At this time, the crusher that can be used is not limited in configuration, but specifically, a vertical crusher, a turbo cutter, a turbo grinder, and a rotary cutter. Any one selected from a group of crushing equipment consisting of a mill), a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter. It may include, but is not limited to, the example described above.

At this time, in the pulverization step, the hydrogel polymer can be pulverized so that the particle size is about 2 to about 10 mm.

It is not technically easy to pulverize the particle size to less than 2 mm due to the high water content of the hydrogel polymer, and the phenomenon of agglomeration between the pulverized particles may appear. On the other hand, when the particle size is pulverized to exceed 10 mm, the effect of increasing the efficiency in the subsequent drying step is slight.

The hydrogel polymer immediately after polymerization, which has been pulverized as described above or has not undergone the pulverization step, is dried. At this time, the drying temperature in the drying step may be about 150 to about 250 ° C. If the drying temperature is less than 150 ° C, the drying time may become excessively long and the physical properties of the finally formed superabsorbent polymer may deteriorate, and if the drying temperature exceeds 250 ° C, only the polymer surface is excessively formed. Fine powder may be generated in the drying step and the subsequent pulverization step, and the physical properties of the finally formed superabsorbent polymer may be deteriorated. Therefore, the drying is preferably carried out at a temperature of about 150 to about 200 ° C, more preferably about 160 to about 180 ° C.

On the other hand, in the case of the drying time, it is carried out for about 20 to about 90 minutes in consideration of process efficiency and the like, but the drying time is not limited to this.

As long as the drying method in the drying step is usually used in the drying step of the hydrogel polymer, it can be selected and used without limitation in its composition. Specifically, the drying stage can be performed by a method such as hot air supply, infrared irradiation, ultra-high frequency irradiation, or ultraviolet irradiation. The water content of the polymer after the progress of such a drying step can be about 0.1 to about 10% by weight.

Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.

The polymer powder obtained after the pulverization step can have a particle size of about 150 to about 850 μm. Specific examples of the crusher used for pulverizing to such a particle size are a pin mill, a hammer mill, a screw mill, a roll mill, and a disc mill (a disc mill). Although disk mills, jog mills, and the like are used, the present invention is not limited to the above-mentioned examples.

Then, in order to control the physical properties of the superabsorbent polymer powder that is finally commercialized after such a pulverization step, it is possible to go through a separate process of classifying the polymer powder obtained after pulverization according to the particle size. The polymer powder can be classified so as to have a constant weight ratio according to the particle size range.

Next, the inorganic filler and the epoxy-based surface cross-linking agent are mixed with the base resin (step 2).

In a general method for producing a superabsorbent polymer, a dried and crushed polymer, that is, a surface cross-linking solution containing a surface cross-linking agent is mixed with a base resin, and then heat is applied to the mixture to raise the temperature. A surface cross-linking reaction is carried out on the pulverized polymer.

The surface cross-linking step is a step of inducing a cross-linking reaction on the surface of the pulverized polymer in the presence of a surface cross-linking agent to form a super absorbent polymer having further improved physical properties. A surface cross-linking layer (surface modification layer) is formed on the surface of the pulverized polymer particles by such surface cross-linking.

Generally, since the surface cross-linking agent is applied to the surface of the superabsorbent resin particles, the surface cross-linking reaction occurs on the surface of the superabsorbent resin particles, which does not substantially affect the inside of the particles. The cross-linking property on the surface of the material is improved. Therefore, the surface-crosslinked superabsorbent polymer particles have a higher degree of cross-linking near the surface inside.

On the other hand, as the surface cross-linking agent, a compound capable of reacting with the functional group of the polymer is used, and as an example, a polyhydric alcohol compound, an epoxy compound, a polyamine compound, a haloepoxy compound, a condensate product of a haloepoxy compound, oxazoline compounds, etc. It is known that valent metal salts, alkylene carbonate compounds, and the like can be used.

On the other hand, according to the production method of the present invention, an epoxy-based surface cross-linking agent is used, and two types of epoxy-based surface cross-linking agents having different epoxy equivalents are mixed and used. When two kinds of epoxy-based surface cross-linking agents are mixed and used in this way, a cross-linking layer is formed as a double layer on the surface of the super absorbent polymer, whereby water does not deteriorate in the rewetting property of the superabsorbent polymer. It is possible to further improve the liquid permeability, which is the property of passing through quickly.

Specifically, in the production method of the present invention, as the epoxy-based surface cross-linking agent, the first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and the second epoxy equivalent having an epoxy equivalent of 130 to 200 g / eq. Use an epoxy crosslinker.

In one embodiment, the first epoxy crosslinker may have an epoxy equivalent in the range of 110-125 g / eq. The first epoxy cross-linking agent is used to obtain the effect of improving the overall water absorption characteristics by the primary surface cross-linking of the base resin, and if the epoxy equivalent of the first epoxy cross-linking agent is less than 100 g / eq, it should be used. The above-mentioned effects cannot be sufficiently ensured.

The first epoxy cross-linking agent is preferably a bifunctional cross-linking agent. When a bifunctional epoxy crosslinker is used as the first epoxy crosslinker, the flexibility of the crosslinked chain can be ensured, thereby maximizing the absorption performance of the superabsorbent polymer.

The content of the first epoxy cross-linking agent may be 0.01 to 0.1 parts by weight, or 0.02 to 0.05 parts by weight with respect to 100 parts by weight of the base resin. If the content of the first epoxy cross-linking agent is less than 0.01 parts by weight with respect to 100 parts by weight of the base resin, sufficient surface cross-linking is not performed, and there is a problem of reduced water absorption capacity and liquid permeability. If it exceeds 0.1 parts by weight, there may be a problem that the rewetting property of the highly water-absorbent resin is deteriorated.

Examples of the first epoxy cross-linking agent include one or more selected from the group consisting of ethylene glycol diglycidyl ether and diethylene glycol diglycidyl ether.

The second epoxy cross-linking agent has a higher epoxy equivalent than the first epoxy cross-linking agent, and the depth of penetration of the second epoxy cross-linking agent at the time of surface cross-linking of the base resin is different from that of the first epoxy cross-linking agent. do. Therefore, when surface cross-linking is performed using the first epoxy cross-linking agent and the second epoxy cross-linking agent at the same time, the effect of double-cross-linking the surface of the base resin can be obtained.

In one embodiment, the epoxy equivalent of the second epoxy crosslinker may be 135 g / eq or higher, 150 g / eq or higher, or 160 g / eq or higher and 195 g / eq or lower, or 190 g / eq or lower. It is not limited to.

The content of the second epoxy cross-linking agent may be 0.001 to 0.1 parts by weight, or 0.005 to 0.05 parts by weight, based on 100 parts by weight of the base resin. If the content of the second epoxy cross-linking agent is less than 0.001 part by weight with respect to 100 parts by weight of the base resin, the double surface cross-linking effect cannot be obtained, and if it exceeds 0.1 parts by weight. There may be a problem that the surface cross-linking strength is excessively strong and the rewetting property is deteriorated.

Examples of the second epoxy cross-linking agent include glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether and polyglyceryl polysyl lycyllyl lycyllyl lycerol. One or more species selected from the group consisting of ether) can be mentioned. The polyglycerol polyglycidyl ether may preferably be a triglycerol polyglycidyl ether having 3 repeating units.

The second epoxy cross-linking agent preferably contains 3 or more or 3 to 4 epoxy functional groups. When the second epoxy cross-linking agent satisfying the number of functional groups is used, only the cross-linking strength of the outermost outer surface of the highly water-absorbent particles can be additionally improved, whereby the liquid permeability and the re-permeability of the high water-absorbent resin can be improved. Wet properties can be further improved.

When the epoxy-based surface cross-linking agent is added, water can be additionally mixed together and added in the form of a surface cross-linking solution. When water is added, there is an advantage that the surface cross-linking agent is uniformly dispersed in the polymer. At this time, the content of the added water is heavy for the purpose of inducing uniform dispersion of the surface cross-linking agent to prevent the aggregation phenomenon of the polymer powder and at the same time optimizing the depth of surface penetration of the surface cross-linking agent. It is preferable to add the mixture in a ratio of about 1 to about 10 parts by weight with respect to 100 parts by weight of the combined product.

On the other hand, in addition to the above-mentioned surface cross-linking agent, one selected from the group consisting of polyvalent metal salts such as aluminum salts, more specifically aluminum sulfates, potassium salts, ammonium salts, sodium salts and hydrochlorides. The above may be further included.

By additionally using such a multivalent metal salt, the liquid permeability of the superabsorbent polymer produced by the method of one embodiment can be further improved. Such a polyvalent metal salt can be added to the surface cross-linking solution together with the surface cross-linking agent, and can be used in a content of 0.01 to 4 parts by weight with respect to 100 parts by weight of the base resin.

Further, in the production method of the present invention, an inorganic filler is mixed with the base resin before the temperature rise for performing the surface modification reaction to impart an anti-aggregation (anti-caking) effect. In the present invention, the inorganic filler is mixed by a dry mixing method before mixing the surface cross-linking solution, in which case the base resin and the inorganic filler are further uniformly mixed.

The inorganic filler can be mixed either hydrophobically or hydrophilicly, and silica particles such as fumed silica and precipitated silica can be used, but the present invention is limited thereto. is not it.

Further, the inorganic filler is added at a concentration of about 0.01 to about 0.5 parts by weight, or about 0.02 to about 0.2 parts by weight with respect to 100 parts by weight of the base resin or superabsorbent polymer. obtain. When the amount of the inorganic filler used exceeds 0.5 parts by weight, absorption characteristics such as pressurized water absorption capacity may deteriorate, and when it is less than 0.01 parts by weight, there is no aggregation preventing effect. From the above viewpoint, it is preferable to use the product in the range of parts by weight.

On the other hand, although the pressurized water absorption capacity and the permeability can be improved by such a surface cross-linking reaction, the rewetting property needs to be further complemented.

According to the production method of the present invention, a hydrophobic substance is mixed with the base resin to further improve the rewetting property before the temperature is raised in order to mix the surface cross-linking agent with the base resin and carry out the surface cross-linking reaction. Can be done. In addition, the surface cross-linking efficiency is improved, and the absorption rate and the liquid permeability can be further improved as compared with the resin which does not use a hydrophobic substance.

As the hydrophobic substance, a substance having an HLB of 0 or more, 1 or more, or 2 or more as its lower limit value and 6 or less, 5 or less, or 5.5 or less as its upper limit value can be used. can. Further, since the hydrophobic substance must be melted during the surface cross-linking reaction and located in the surface modification layer of the base resin, it is possible to use a substance whose melting point is equal to or lower than the reaction temperature of the surface cross-linking. can.

Examples of the hydrophobic substances that can be used include glyceryl stearate, glycol stearate, magnesium stearate, glyceryl laurate, and sorbitan stearate. , Sorbitan trioleate, PEG-4 dilaurate, etc., preferably glyceryl stearate, or glyceryl laurate, but the present invention is not limited thereto. No.

The hydrophobic substances are distributed in the surface modification layer on the surface of the base resin, and the swelled resin particles aggregate with each other due to the increased pressure in the process of the highly water-absorbent resin absorbing the liquid and swelling. By preventing solidification and imparting hydrophobicity to the surface, it is possible to facilitate the permeation and diffusion of the liquid. Therefore, it can contribute to the improvement of the rewetting property of the super absorbent polymer.

The hydrophobic substance is about 0.001 part by weight or more, about 0.005 part by weight or more, or about 0.01 part by weight or more, and about 0.5 part by weight with respect to 100 parts by weight of the base resin. It can be mixed below, or about 0.3 parts by weight or less, or about 0.1 parts by weight or less. If the content of the hydrophobic substance is excessively small, it is not enough to improve the rewetting property, and if it is excessively contained, the base resin and the hydrophobic substance are desorbed from each other and there is no effect of improving rewetting, or impurities. From this point of view, the weight range is preferable.

The method for mixing the hydrophobic substance with the base resin is not particularly limited, but the superabsorbent polymer particles are mixed by a method in which the hydrophobic substance is dispersed in the surface cross-linking solution together with the surface cross-linking agent and mixed with the base resin. It is preferable because it can be coated more uniformly.

Next, a surface modification step is performed on the base resin by applying heat to the mixture of the base resin and the epoxy-based surface cross-linking agent to raise the temperature (step 3).

The surface modification step is carried out by heating at a temperature of about 120 to about 190 ° C., preferably about 130 to about 180 ° C. for about 10 to about 90 minutes, preferably about 20 to about 70 minutes. If the crosslinking reaction temperature is less than 120 ° C or the reaction time is too short, the surface crosslinking reaction does not occur correctly and the permeability becomes low, and if it exceeds 190 ° C or the reaction time is too long, the retention capacity decreases. Can be.

The heating means for the surface modification reaction is not particularly limited. A heat medium can be supplied, or a heat source can be directly supplied for heating. At this time, as the type of heat medium that can be used, steam, hot air, a heated fluid such as hot oil, or the like can be used, but the present invention is not limited to this, and the heat medium to be supplied is also used. The temperature can be appropriately selected in consideration of the means of the heat medium, the rate of temperature rise and the target temperature of temperature rise. On the other hand, examples of the heat source directly supplied include heating by electricity and heating by gas, but the present invention is not limited to the above-mentioned examples.

By the surface modification step as described above, a double surface cross-linking structure formed by reacting two different epoxy-based surface cross-linking agents with the functional groups of the base resin is formed on the surface of the base resin. , A surface-modified layer in which the above-mentioned hydrophobic substance and the inorganic filler are uniformly distributed can be formed in the surface crosslinked structure.

Therefore, the highly water-absorbent resin produced by the production method of the present invention has improved rewetting and liquid passage without deteriorating physical properties such as retention ability and pressure water absorption ability by such a double surface modification layer. Can have sex.

Therefore, according to another embodiment of the present invention, a base resin containing a crosslinked polymer in which an acrylic acid-based monomer in which at least a part of acidic groups is neutralized is crosslinked and polymerized; and particles of the base resin. The cross-linked polymer comprises a double surface-modified layer formed on the surface and additionally cross-linked via two types of epoxy-based surface cross-linking agents having different epoxy equivalents, and the surface-modified layer includes a double surface-modified layer. The two epoxy-based surface cross-linking agents containing an inorganic filler include a first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq, and a second epoxy cross-linking agent having an epoxy equivalent of 130 to 200 g / eq. A highly water-absorbent resin comprising an agent is provided.

A detailed description of the specific manufacturing method and physical properties of the superabsorbent polymer is as described above in the superabsorbent polymer manufacturing method.

The super absorbent polymer has a centrifugal separation retention capacity (CRC) measured in accordance with the EDANA method WSP 241.3 of about 25 g / g or more, or about 29 g / g or more, or about 30 g / g or more. And it can have a range of about 40 g / g or less, or about 38 g / g or less, or about 35 g / g or less.

Further, the super absorbent polymer has a pressurized water absorption capacity (AUP) of 0.3 psi measured in accordance with the EDANA method WSP 242.3 of about 20 g / g or more, about 23 g / g or more, or about 25 g. It can have a range of more than / g and less than or equal to about 37 g / g, or less than or equal to about 35 g / g, or less than or equal to about 32 g / g.

Further, the superabsorbent polymer may have an absorption time of 40 seconds or less, 35 seconds or less, or about 32 seconds or less. The smaller the value, the better the absorption rate, and the lower limit of the absorption rate is theoretically 0 seconds, but as an example, it may be about 5 seconds or more, or about 10 seconds or more, or about 12 seconds or more.

The absorption rate means the time (time, unit: second) at which the liquid vortex disappears due to rapid absorption when a highly water-absorbent resin is added to physiological saline and stirred. It can be seen that the shorter the time, the faster the water-absorbent resin has a faster initial absorption rate.

Further, the superabsorbent polymer may have a permeability (permeability, unit: second) measured by the following formula 1 of about 35 seconds or less, or about 30 seconds or less. The smaller the value, the better the liquid permeability, and the theoretical lower limit is 0 seconds, but it may be, for example, about 5 seconds or more, or about 10 seconds or more, or about 12 seconds or more.

In the above formula 1,
For T1, put 0.2 ± 0.0005 g of a classified (300 to 600 μm) highly water-absorbent resin sample in a chromatography tube, add salt water to make the salt water volume 50 mL, leave it for 30 minutes, and then liquid. It is the time it takes for the surface height to decrease from 40 mL to 20 mL, and B is the time it takes for the liquid level height to decrease from 40 mL to 20 mL in a chromatographic tube filled with salt water.

Further, the superabsorbent polymer can exhibit further improved rewetting characteristics while exhibiting excellent absorption characteristics.

More specifically, after immersing 4 g of the highly water-absorbent resin in 200 g of tap water and inflating it for 2 hours, the swollen high water-absorbent resin is left on a filter paper for 1 minute under a pressure of 0.75 psi. Then, the rewetting property (long-term rewetting of pressurized tap water) defined by the weight of water that has re-exuded from the highly water-absorbent resin into the filter paper is 1.0 g or less, or 0.9 g or less, or It can be 0.8 g or less. The smaller the value of the water, the better, and the theoretical lower limit is 0 g, but it can be, for example, 0.1 g or more, 0.2 g or more, or 0.3 g or more.

The tap water used in the rewetting property evaluation has an electric conductivity of 140 to 150 μS / cm. Since the electric conductivity of tap water has a great influence on the measured physical properties, it is necessary to measure the physical properties such as rewetting using tap water having the same level of electric conductivity.

As described above, the superabsorbent polymer of the present invention has an excellent absorbency and can suppress the rewetting and urine leakage phenomena even when a large amount of urine is absorbed.

The present invention will be described in more detail with reference to the following examples. However, the following examples merely illustrate the present invention, and the detailed description of the present invention is not limited to the following examples.

[Manufacturing of super absorbent polymer]
(Example 1)
(1) Production of base resin 518 g of acrylic acid, 3.2 g of polyethylene glycol diacrylate (400) diacrylate, and diphenyl (2,4,6-) in a 3 L glass container equipped with a stirrer, nitrogen input device, and thermometer. After adding 0.04 g of trimethylbenzoyl) -phosphine oxide to dissolve it, add 822.2 g of a 24.5% sodium hydroxide solution to continuously add nitrogen to make a water-soluble unsaturated monomer aqueous solution. Manufactured. The aqueous solution of the water-soluble unsaturated monomer was cooled at 40 ° C. 500 g of this aqueous solution is added to a stainless steel container having a width of 250 mm, a length of 250 mm and a height of 30 mm, and irradiated with ultraviolet rays (irradiation amount: 10 mV / cm ² ) to carry out UV polymerization for 90 seconds to obtain a hydrogel-like polymer. bottom. After crushing the obtained hydrogel-like polymer to a size of 2 mm * 2 mm, the obtained gel-like resin is spread on a stainless steel wire mesh having a pore size of 600 μm to a thickness of about 30 mm and placed in a 180 ° C. hot air oven for 30 minutes. It was dry. The dried polymer thus obtained was pulverized using a pulverizer and classified by an ASTM standard standard mesh sieve to obtain a base resin having a particle size of 150 to 850 μm.

(2) Production of highly water-absorbent resin After mixing 0.1 part by weight of silica dryly with 100 parts by weight of the base resin, 0.02 part by weight of ethylene glycol diglycidyl ether (epoxy equivalent 113 to 125 g / eq), glycerol. Polyglycidyl ether (epoxy equivalent 135-155 g / eq, trifunctional) 0.01 parts by weight, 6.2 parts by weight of water, 0.2 parts by weight of aluminum sulfate, 0.03 parts by weight of glyceryl stearate (HLB 3.8) A surface cross-linking solution containing a portion was sprayed and mixed, and this was placed in a container consisting of a stirrer and a double jacket to carry out a surface cross-linking reaction at 140 ° C. for 35 minutes. Then, the surface-treated powder was classified by an ASTM standard mesh sieve to obtain a superabsorbent polymer powder having a particle size of 150 to 850 μm.

(Example 2)
A highly water-absorbent resin powder was obtained by the same method as in Example 1 except that glycerol polyglycidyl ether was used in an amount of 0.005 part by weight based on 100 parts by weight of the base resin in the step (2).

(Example 3)
A highly water-absorbent resin powder was obtained by the same method as in Example 1 except that glycerol polyglycidyl ether was used in an amount of 0.03 part by weight based on 100 parts by weight of the base resin in the step (2).

(Example 4)
A highly water-absorbent resin powder was obtained in the same manner as in Example 1 except that glycerol polyglycidyl ether was used in an amount of 0.05 parts by weight based on 100 parts by weight of the base resin in the step (2).

(Example 5)
Example 1 and Example 1 except that polyglycerol polyglycidyl ether (epoxy equivalent 168 g / eq) was used in 0.01 parts by weight with respect to 100 parts by weight of the base resin in the step (2) instead of glycerol polyglycidyl ether. A highly water-absorbent resin powder was obtained by the same method.

(Example 6)
Example 1 except that sorbitol polyglycidyl ether (epoxy equivalent 160 to 190 g / eq) was used in 0.01 parts by weight with respect to 100 parts by weight of the base resin in the step (2) instead of glycerol polyglycidyl ether. A highly water-absorbent resin powder was obtained in the same manner as in the above method.

(Comparative Example 1)
(1) Production of base resin 518 g of acrylic acid, 3.2 g of polyethylene glycol diacrylate (400) diacrylate, and diphenyl (2,4,6-) in a 3 L glass container equipped with a stirrer, nitrogen input device, and thermometer. After adding 0.04 g of trimethylbenzoyl) -phosphine oxide to dissolve it, add 822.2 g of a 24.5% sodium hydroxide solution to continuously add nitrogen to make a water-soluble unsaturated monomer aqueous solution. Manufactured. The aqueous solution of the water-soluble unsaturated monomer was cooled at 40 ° C. 500 g of this aqueous solution is added to a stainless steel container having a width of 250 mm, a length of 250 mm and a height of 30 mm, and irradiated with ultraviolet rays (irradiation amount: 10 mV / cm ² ) to carry out UV polymerization for 90 seconds to obtain a hydrogel-like polymer. bottom. After crushing the obtained hydrogel-like polymer to a size of 2 mm * 2 mm, the obtained gel-like resin is spread on a stainless steel wire mesh having a pore size of 600 μm to a thickness of about 30 mm and placed in a 180 ° C. hot air oven for 30 minutes. It was dry. The dried polymer thus obtained was pulverized using a pulverizer and classified by an ASTM standard standard mesh sieve to obtain a base resin having a particle size of 150 to 850 μm.

(2) Production of highly water-absorbent resin After mixing 0.1 part by weight of silica dryly with 100 parts by weight of the base resin, 0.02 part by weight of ethylene glycol diglycidyl ether (epoxy equivalent 113 to 125 g / eq), water. A surface cross-linked solution containing 6.2 parts by weight, 0.2 parts by weight of aluminum sulfate, and 0.03 parts by weight of glyceryl stearate (HLB 3.8) is sprayed and mixed, and this is mixed by a container consisting of a stirrer and a double jacket. The surface cross-linking reaction was carried out at 140 ° C. for 35 minutes. Then, the surface-treated powder was classified by an ASTM standard mesh sieve to obtain a superabsorbent polymer powder having a particle size of 150 to 850 μm.

(Comparative Example 2)
A highly water-absorbent resin powder was obtained in the same manner as in Comparative Example 1 except that ethylene glycol diglycidyl ether was used in an amount of 0.03 part by weight based on 100 parts by weight of the base resin in the step (2).

(Comparative Example 3)
A highly water-absorbent resin powder was obtained in the same manner as in Comparative Example 1 except that ethylene glycol diglycidyl ether was used in an amount of 0.05 parts by weight based on 100 parts by weight of the base resin in the step (2).

<Experimental example>
The physical properties of the superabsorbent polymers produced in the above Examples and Comparative Examples were evaluated by the following methods.

Unless otherwise stated, all of the following physical property evaluations are performed at constant temperature and humidity (23 ± 1 ° C., relative humidity 50 ± 10%), and for physiological saline or salt water, use a 0.9 wt% sodium chloride (NaCl) aqueous solution. means.

The tap water used in the following re-wet property evaluation was one having an electrical conductivity of 140 to 150 μS / cm when measured using Orion Star A222 (manufactured by Thermo Scientific).

(1) Centrifugal Retention Capacity (CRC)
The holding capacity of each resin under no load absorption ratio was measured according to EDANA WSP 241.3.

Specifically, the super absorbent polymer W ₀ (g) (about 0.2 g) is uniformly placed in a non-woven fabric envelope, sealed, and then made into physiological saline (0.9% by weight) at room temperature. It was flooded. After 30 minutes, the envelope was drained for 3 minutes under the condition of 250 g using a centrifuge, and the mass W ₂ (g) of the envelope was measured. Further, after performing the same operation without using a resin, the mass W ₁ (g) at that time was measured. Using each mass obtained, CRC (g / g) was calculated by the following formula.

(2) Absorption rate (Vortex time)
The absorption time was measured in seconds according to the method described in International Publication No. 1987-003208.

Specifically, 2 g of highly water-absorbent resin is put in 50 mL of physiological saline at 23 ° C., and the magnet bar (diameter 8 mm, length 30 mm) is stirred at 600 rpm until the vortex disappears. Calculated by measuring in seconds.

(3) Pressurized water absorption capacity (AUP: Absorption Under Pressure)
The pressurized water absorption capacity of 0.3 psi of each resin was measured according to the EDANA method WSP 242.3.

Specifically, a stainless steel 400 mesh wire mesh was attached to the bottom of a plastic cylinder having an inner diameter of 60 mm. _{The outer diameter of the piston that can evenly spray the highly water-absorbent resin W 0} (g) (0.90 g) on the wire mesh under the conditions of normal temperature and humidity 50% and further apply a load of 0.3 psi evenly on it. It is slightly smaller than 60 mm, and there is no gap with the inner wall of the cylinder so that the vertical movement is not hindered. At this time, the weight W ₃ (g) of the device was measured.
A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a Petri dish having a diameter of 150 mm so that a saline solution composed of 0.9% by weight sodium chloride was at the same level as the upper surface of the glass filter. A sheet of filter paper having a diameter of 90 mm was placed on it. The measuring device was placed on a filter paper, and the liquid was absorbed under a load for 1 hour. After 1 hour, the measuring device was lifted and its weight W ₄ (g) was measured.

The pressurized water absorption capacity (g / g) was calculated by the following formula using each mass obtained.

(4) Permeability
Lines were displayed on the liquid levels of 20 mL and 40 mL with the piston placed in the chromatography tube (F20 mm). After that, water is poured in the opposite direction so that bubbles do not occur between the glass filter at the bottom of the chromatography tube and the cock, fill about 10 mL, wash with salt water 2-3 times, and 0.9% salt water up to 40 mL or more. Meet. The time (B) was recorded when the piston was placed in the chromatography tube and the lower valve was opened and the liquid level decreased from 40 mL to the 20 mL display line.

Leave 10 mL of salt water in the chromatography tube, add 0.2 ± 0.0005 g of the classified (300 to 600 μm) highly water-absorbent resin sample, add salt water to make the salt water volume 50 mL, and then leave it for 30 minutes. .. Then, a piston with a weight (0.3 psi = 106.26 g) is placed in the chromatography tube and left for 1 minute, and then the lower valve of the chromatography tube is opened to reduce the liquid level from 40 mL to the 20 mL display line (T1). Was recorded, and the time (unit: seconds) of T1-B was calculated.

(5) Long-term rewetting of pressurized tap water (2hrs)
(1) 4 g of a highly water-absorbent resin was uniformly sprinkled on a Petri dish having a diameter of 13 cm, dispersed, and 200 g of tap water was poured and then swollen for 2 hours.

(2) A highly water-absorbent resin that has been swollen for 2 hours is laid on 20 sheets of filter paper (catalog No. 1004-110, pore size 20-25 μm, diameter 11 cm) manufactured by hatman, and a weight of 11 cm in diameter and 5 kg (0). Pressurized at .75 psi) for 1 minute.

(3) After pressurizing for 1 minute, the amount of tap water (unit: g) attached to the filter paper was measured.

The physical property values of the Examples and Comparative Examples are shown in Table 1 below.

With reference to Table 1, it can be confirmed that all of Examples 1 to 6 of the present invention exhibit excellent rewetting properties and liquid permeability. On the other hand, it can be seen that Comparative Examples 1 and 2 using only the first epoxy cross-linking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq are not better in liquid permeability and rewetting characteristics than the examples. That is, when comparing the cases where the same amount of the epoxy-based surface cross-linking agent was used, it was confirmed that the case of the example showed excellent liquid permeability and rewetting characteristics as compared with the comparative example.

Claims (13)

A step of preparing a base resin (base resin) having an acidic group and having an acrylic acid-based monomer in which at least a part of the acidic group is neutralized and an internal cross-linking agent cross-linked and polymerized (step 1);
The base resin, an inorganic filler, e epoxy based surface crosslinking agent and a mixture of polyvalent metal salt, the inorganic filler were mixed in dry forward to the base resin, followed by an epoxy-based surface-crosslinking agent and a polyvalent metal salt It comprises a step of dissolving in water and mixing in a surface crosslinked solution state (step 2); and a step of raising the temperature of the mixture of the step 2 to perform surface modification on the base resin (step 3).
The epoxy surface crosslinking agent state, and are not the first epoxy crosslinking agent and an epoxy equivalent of the epoxy equivalent is less than 100 g / eq or more 130 g / eq includes a second epoxy crosslinking agent is a 130~200g / eq,
The first epoxy cross-linking agent is contained in an amount of 0.02 to 0.05 parts by weight based on 100 parts by weight of the base resin, and the second epoxy cross-linking agent is contained in an amount of 0.005 to 0.05 parts by weight based on 100 parts by weight of the base resin. A method for producing a superabsorbent polymer contained in a part. The highly water-absorbent resin according to claim 1 , wherein the first epoxy cross-linking agent is one or more selected from the group consisting of ethylene glycol diglycidyl ether and diethylene glycol diglycidyl ether. Production method. The second epoxy cross-linking agent is glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether (polyglyceryl polyester) The method for producing a highly water-absorbent resin according to claim 1 or 2 , which is one or more selected from the group. The method for producing a superabsorbent polymer according to any one of claims 1 to 3 , wherein in the step 2, a hydrophobic substance having an HLB of 0 or more and 6 or less is further mixed. The hydrophobic substances include glyceryl stearate, glycol stearate, magnesium stearate, glyceryl laurate, sorbitan stearate, and sorbitan stearate. The method for producing a highly water-absorbent resin according to claim 4 , which comprises at least one selected from the group consisting of sterbitan trioleate) and PEG-4 dilaurate. The method for producing a highly water-absorbent resin according to claim 4 or 5 , wherein the hydrophobic substance is mixed in an amount of 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the base resin. The method for producing a superabsorbent polymer according to any one of claims 1 to 6 , wherein the step 3 is performed at a temperature of 120 to 190 ° C. The first step is
A water-containing gel-like polymer is formed by polymerizing a monomer composition having an acidic group and containing at least a part of the acidic group neutralized with an acrylic acid-based monomer, an internal cross-linking agent, and a polymerization initiator. step;
The stage of drying the hydrogel polymer;
The method for producing a superabsorbent polymer according to any one of claims 1 to 7 , which comprises a step of pulverizing the dried polymer; and a step of classifying the pulverized polymer. A base resin containing a crosslinked polymer in which an acrylic acid-based monomer in which at least a part of an acidic group is neutralized is crosslinked and polymerized; and the crosslinked polymer is formed on the particle surface of the base resin and has an epoxy equivalent. Includes a double surface modification layer that is additionally crosslinked via two different epoxy-based surface crosslinkers.
The surface modification layer contains an inorganic filler and a polyvalent metal salt and contains.
The two epoxy-based surface-crosslinking agent is seen containing an epoxy equivalent second epoxy crosslinking agent first epoxy crosslinking agent and an epoxy equivalent weight less than 100 g / eq or more 130 g / eq is 130~200g / eq,
The first epoxy cross-linking agent is contained in an amount of 0.02 to 0.05 parts by weight based on 100 parts by weight of the base resin, and the second epoxy cross-linking agent is contained in an amount of 0.005 to 0.05 parts by weight based on 100 parts by weight of the base resin. Super absorbent polymer contained in the part. The superabsorbent polymer according to claim 9 , wherein the superabsorbent polymer has an absorption time of 40 seconds or less. The superabsorbent polymer according to claim 9 or 10 , wherein the superabsorbent polymer has a permeability (unit: second) measured by the following formula 1 of 35 seconds or less.

In the above formula 1,
For T1, put 0.2 ± 0.0005 g of a classified (300 to 600 μm) highly water-absorbent resin sample in a chromatography tube, add salt water to make the salt water volume 50 mL, leave it for 30 minutes, and then liquid. It is the time it takes for the surface height to decrease from 40 mL to 20 mL, and B is the time it takes for the liquid level height to decrease from 40 mL to 20 mL in a chromatographic tube filled with salt water. The superabsorbent polymer according to any one of claims 9 to 11 , wherein the superabsorbent polymer has a centrifugation retention capacity (CRC) of 25 g / g or more. The highly water-absorbent resin is obtained by immersing 4 g of the highly water-absorbent resin in 200 g of tap water and inflating it for 2 hours, and then leaving the swollen high water-absorbent resin on a filter paper for 1 minute under a pressure of 0.75 psi. Then, claim 9 to the rewetting property (long-term rewetting of pressurized tap water) defined by the weight of water that has exuded from the highly water-absorbent resin into the filter paper again is 1.0 g or less. The highly water-absorbent resin according to any one of 12.